I think you may need to remove the interaction between Graves and this item. Reducing the CD of a 70% AS steroid and most importantly a dash by 6 second per AA is ridiculous. He will have a permanent 70% AS and dash as often as Vayne can tumble.

Haven't read through all the posts but good Lord, does this mean Janna's shield effectively increases ranged AD by 100? It should be +50 on the targetted enemy and then + 0.5(50+50) for the two additional enemies correct?

Yes, this basically means that Janna + an AD Carry that works well with this item will be exceptionally lethal.